I've been having trouble with rpm seg faults and yum freezing ever since upgrading to Fedora Core 6. For example:

.....
extras                    100% |=========================| 1.1 kB    00:00     
Reading repository metadata in from local files
zsh: segmentation fault  sudo yum -y update rpm

and this:

% sudo rpmdb --rebuilddb
zsh: segmentation fault  sudo rpmdb --rebuilddb

To get rpm to start working again, I've been resorting to doing this, which fixes the problems most of the time:

% sudo rm -f /var/lib/rpm/__db.00* ; sudo rpmdb --rebuilddb

This has failed to work on one occasion:

% sudo rm -f /var/lib/rpm/__db.00* ; sudo rpmdb --rebuilddb
Password:
zsh: segmentation fault  sudo rpmdb --rebuilddb

It looks like the hangs might be some kind of locking bug -- I've also seen these programs hang on futex(), where rebooting seems to help get them back into a working state. I'll just assume that this will get fixed at some point.

Update (2006 November 28): Database problems have continued:

% sudo rpmdb --rebuilddb
rpmdb: PANIC: fatal region error detected; run recovery
error: db4 error(-30977) from dbenv->open: DB_RUNRECOVERY: Fatal error, run database recovery
error: cannot open Packages index using db3 -  (-30977)

the workaround described above seemed to fix it.